This invention relates to an article counter or sensor for sensing and counting articles such as seeds flowing in a chute in a seed planter and, in particular, to the signal processing unit of such a sensor.
Optical seed sensors in which a seed interrupts a radiation or light beam are known in the art. Such systems are described in U.S. Pat. Nos. 4,163,507 (Bell), 3,537,091 (Schenkenberg), 3,928,751 (Fathauer), 3,723,989 (Fathauer et al), 4,166,948 (Steffen), 3,974,377 (Steffen) and 4,246,469 (Merlo). For a number of reasons, such seed sensors have been inaccurate. One problem has been the spatial non-uniformity of the light source and/or of the light detectors so that signals generated by the light detectors vary, depending upon what portion of the light beam is interrupted. Another problem is that such sensors have usually been coupled to circuits, such as the differentiating circuit of U.S. Pat. No. 4,163,507, which essentially count pulses in the detector output and therefore, such systems count a plurality of seeds simultaneously traversing the light beam as a single seed.